1. Field of the Invention
The present invention relates to wireless communications, more particularly, to a method and apparatus for transmitting a synchronization signal in a wireless communication system.
2. Related Art
The next-generation multimedia wireless communication systems which are recently being actively researched are required to process and transmit various pieces of information, such as video and wireless data as well as the initial voice-centered services. The 4th generation wireless communication systems which are now being developed subsequently to the 3rd generation wireless communication systems are aiming at supporting high-speed data service of downlink 1 Gbps (Gigabits per second) and uplink 500 Mbps (Megabits per second). The object of the wireless communication system is to establish reliable communications between a number of users irrespective of their positions and mobility. However, a wireless channel has abnormal characteristics, such as path loss, noise, a fading phenomenon due to multi-path, inter-symbol interference (ISI), and the Doppler Effect resulting from the mobility of a user equipment. A variety of techniques are being developed in order to overcome the abnormal characteristics of the wireless channel and to increase the reliability of wireless communication.
Meanwhile, with the employment of machine-to-machine (M2M) communication and with the introduction and distribution of various devices such as a smart phone, a table personal computer (PC), etc., a data requirement size for a cellular network is increased rapidly. To satisfy a high data requirement size, various techniques are under development. A carrier aggregation (CA) technique, a cognitive radio (CR) technique, or the like for effectively using more frequency bands are under research. In addition, a multiple antenna technique, a multiple base station cooperation technique, or the like for increasing data capacity within a limited frequency are under research. That is, eventually, the wireless communication system will be evolved in a direction of increasing density of nodes capable of accessing to an area around a user. A wireless communication system having nodes with higher density can provide a higher performance through cooperation between the nodes. That is, a wireless communication system in which each node cooperates has a much higher performance than a wireless communication system in which each node operates as an independent base station (BS), advanced BS (ABS), node-B (NB), eNode-B (eNB), access point (AP), etc.
A distributed multi-node system (DMNS) comprising a plurality of nodes within a cell may be used to improve performance of a wireless communication system. The DMNS may include a distributed antenna system (DAS), a radio remote head (RRH), and so on. Also, standardization work is underway for various multiple-input multiple-output (MIMO) techniques and cooperative communication techniques already developed or applicable in a future so that they can be applied to the DMNS.
The base station may transmit a synchronization signal to the user equipment, and the user equipment may synchronize time and frequency based on the received synchronization signal. In the distributed multi-node system, multiple nodes may transmit the synchronization signal. It is necessary that the user equipment synchronizes based on the synchronization signal of the node which serves the user equipment among the synchronization signals transmitted by the multiple nodes.
Accordingly, a method in which the user equipment performs synchronization effectively in the distributed multi-node system is required.